1. Field of the Invention
This invention relates to the apparatus of the type that the gravitational moving solid particle is reacting with the radial flow fluid. The components in the radial flow fluid react with the moving solid particle such as catalyst.
2. Description of the Prior Art
The radial flow reactor and regenerator are well known in the art for hydrocarbon processing in the petroleum and petrochemical industry. The radial reactor and regenerator are annular contactors in which catalyst particle bed is held in place by two concentric cylindrical particle retaining screens. The radial flow reactor is shown, for instance, by U.S. Pat. Nos. 3,927,987; 3,907,511; 3,882,015; 3,799,866, 3,785,963 and 3,692,496. The radial flow regenerator is shown, for instance, by U.S. Pat. Nos. 3,652,231 and 3,647,680. This type of radial flow contactor provides the benefits over the other conventional contactors in that the pressure drop across the radial flow contactor is lower, which reduces the recycle compressor capital and utility requirement. To convert the hydrocarbons into useful products, the temperature and pressure are carefully controlled in these radial flow reactors. Invariably the catalysts used in the reactor become deactivated for one or more reasons. One of the most common reasons for deactivation is the accumulation of coke on the catalyst. To restore the performance of the deactivating catalyst, careful reconditioning of the catalyst and burning of the accumulated coke is frequently done. The catalyst is reactivated by contacting of the coke containing catalyst at high temperature with an oxygen containing gas to combust in a regenerator where the catalyst with coke is moving through a radial bed vertically and with oxygen containing gas flowing radially across it. In the continuous or semi-continuous regeneration process, coke laden catalyst particles are at least periodically added and withdrawn from a bed where the coke is combusted. The oxygen containing gas and catalyst with coke reacts in an annular bed. U.S. Pat. No. 3,652,231 shows regeneration apparatus for a continuous catalyst regeneration process. This regeneration apparatus is used in the catalytic reforming of hydrocarbons in a constant-width movable bed of catalyst. U.S. Pat. Nos. 3,647,680 and 3,692,496 also deal with regeneration of reforming catalyst.
A great deal of research and development has been made to improve the design and efficiency of the radial flow reactor/regenerator. U.S. Pat. No. 6,103,652 discloses a staged combustion process and apparatus for regenerating a catalyst in a moving bed that includes at least two separate successive combustion zones. In order to ensure uniform flow of catalyst in the annular bed in the radial flow reactor, a number of the catalyst withdrawal systems employed at the bottom of the catalyst bed are used with centrally located catalyst passages. Typically these have consisted of a number of catalyst withdrawal conduits located below the two catalyst retention screens, with the upper end of each conduit being covered by a conical cap designed to allow equal catalyst flow from every direction. This is shown in U.S. Pat. Nos. 3,706,536, 3,785,963, 3,854,887 and 4,110,081. U.S. Pat. No. 5,157,181 discloses a radial flow reactor with greater annular bed depth in the lower section than upper section in order to maintain near constant catalyst active site. U.S. Pat. No. 4,859,643 discloses a method for regenerating coke containing catalyst particles that confines particles in the combustion section of a regenerator zone to a tapered bed configuration. The tapered bed minimizes surface area loss of the catalyst by increasing the catalyst particle velocity in the high temperature zone and reduces the time that catalyst is exposed to high temperature. This method increases the particle downward velocity in the top section that has a thinner bed depth.
As shown in the previous references, most of the efforts in the prior art are made to achieve uniform solid flow and eliminate the dead spaces between the annular bed. Some vary the catalyst particle velocities at different axial elevation in the annular bed by using tapered bed configuration. The particle velocity increases in the axial direction as the radial bed depth decreases but the particle velocity is similar radially at the same axial elevation. The fluid traverses across the radial bed is maldistributed with the higher flow rate at the thinner section of the bed. This can govern the design of moving bed because the high cross flow rate can stop the catalyst moving by pinning the catalyst against the retaining wall and higher flow rate in the thinner bed section may lead to adverse effect in reaction. Therefore, it is important to develop a novel method and apparatus to optimize the reaction efficiency without significantly impacting the traverse flow pattern and leading to maldistribution of traverse flow.